The invention relates to a driving hub for a vehicle and particularly to a driving hub with a friction gear the reduction ratio of which is infinitely variable adjustable.
Known from U.S. Pat. No. 4,735,430 is a driving hub for a bicycle, of which the hub sleeve, rotatably mounted in the bicycle frame, is driven by a friction gear disposed in the hub sleeve with a hub axle rotatingly driven by the pedals. Two toroidal discs disposed on the axle are coupled to each other frictionally by a plurality of friction wheels. The friction wheels are rotatably mounted on king pins which are in turn pivotally mounted on a stationary friction wheel carrier. One of the two toroidal discs is non-rotatable but is axially displaceable on the hub axle and is pressed against the friction wheels by an expanding coupling provided with sloping thrust faces, as soon as the hub axle is driven. The other toroidal disc which is rotatably disposed on the hub axle is connected to the hub sleeve by a free wheel coupling and a planetary gear mechanism with stationary planet wheels. For infinitely variable adjustment of the transmission ratio of the friction gear, the king pins of the friction wheels are extended radially outwardly and engage sloping thrust slots in a control sleeve enclosing the friction gear and mounted to rotate within the hub sleeve. By rotation of the control sleeve by means of a traction cable arrangement, the angular position of the friction wheels in relation to the hub axle and thus the transmission ratio of the friction gear can be altered.
In the case of the prior art driving hub, the hub sleeve is radially guided on a housing of the friction gear via the control sleeve. In this case, the wheel loading makes adjustment of the transmission ratio difficult. In the case of the known driving hub, since both toroidal discs have to be movably guided, there are not only production problems but also the operational reliability and effective life are undesirable influenced. Finally, the known driving hub calls for special fitting means, since the hub axle has to be rotatably mounted in the bicycle frame, otherwise than with conventional driving hubs. Control via the interposed control sleeve is a complicated non-standard construction. The planetary gearing is absolutely essential in order that the hub sleeve can be driven in the direction of rotation of the driver; however, this impairs the efficiency of the driving hub and increases the hub weight as well as the costs of construction.
An improvement on this hub is disclosed by EP 0 432 742 Al As is conventional with bicycles, the hub axle is adapted to be rigidly fitted into the bicycle frame, with a linkage to the friction gear control passing through the hollow hub axle. The driver is rotationally rigidly connected to the friction wheel carrier and drives a second toroidal disc in that, shifted up to high speed, the friction wheels roll on the first toroidal disc which is rotationally rigidly connected to the hub axle. The king pins which point towards the axle center and which are pivotable in the axle plane are of spherical construction at their inner end and are guided in the outer ring of a ball bearing which, by means of a thrust block, can be moved axially to and fro by the linkage which extends through the hollow hub axle. The second toroidal disc, running at a higher rotary speed, is shifted back to low speeds by a downstream planetary gearing.